Maybe they are more effective for some bodys than for others like many exercises can be, but in my experience i dont think they do a great deal for me perhaps because of my body type. i just think there are better ways to develop the fast twitch fibres which my body responds to much better, ive always liked a more scientific approach to training since i was lifting weights a few years ago and was always interested in hearing new theorys on better ways to stimulate the muscles more completely, the muscle fibre is like a chain each ''link'' in turn will contract when it recieves the message depending on what position the muscle is what determines how many fibres and how many links in the stimulated fibre will hear that message and contract depending on the position of the muscle not all links in the stimulated fibre will hear the message, if you can put the muscle in the favourable position where most recruitment (clearer messages are sent)can be gained then more ''links'' in the fibres will contract, i would consider it a much more complete stimulation for the fast twitch fibres, which then brings me back to what i said in an earlier post technique and how good technique can out do muscle development in my opinion of it all however it does not mean muscle development should be ignored as both are what contributes to the final explosiveness of the muscle, hope im not giving too much away scrap